Picture broadcasting system



Jan. 3, 1939. A. WEAVER PICTURE BROADCASTING' SYSTEM Filed July 7, 1954 6 Sheets-Sheet 1 m. GP*

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vArron/vnf v .vwo E l Jan. 3, 1939 A. WEAVER I PICTURE BROADGASTIG SYSTEM 6 Sheets-Shea?l 2 Filed .Julyl 7, 1954.

/NVEA/TOR A. WEAVER ATTORNEY Jan. 3, 1939. A. WEAVER 2,142,339

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A'. WEAVER l PICTURE BROADCASTING SYSTEM Filed July 7, 1934 6 Sheets-Sheet 4,

/Nl/EA/TR WEA VER ATTORNEY Jan.3,1939; AWE/WER I2,142,339

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Jan. 3, 1939. A, WEAVER. 2,142,339

PICTURE BROADCASTING SYSTEM Filed July 7, 1934 6 sheets-#sheet e /NVE/VTOR A WEAVER f 54 4 T rom/5y Patented Jan. 3, 1939 UNITED STATES PATENT FFCE PICTURE BROADCASTING SYSTEM Application July 7, 1934, Serial No. 734,152

7 Claims.

This invention relates to signalling systems and methods and particularly to a system for broadcasting pictures.

An object of the invention is to provide a system for broadcasting pictures, particularly over telephone lines, which is simple to operate and capable of reproducing pictures of high quality.

In the picture broadcasting system shown and described herein for the purpose of illustration, a picture may be transmitted from any station to each of the other stations of the system or, if desired, to a number of other stations less than the total number. Each station is provided with picture transmitting and receiving apparatus and telephone transmitting and receiving apparatus.

The telephone receiver may be of the loud-speaking type. At each station there is provided a key of the non-locking type which, when operated, causes the transmission of a direct control current which is utilized to control apparatus along thetransmission path to the other stations so that telephone or picture signalling current can be transmitted in one direction only from the first station to the distant station.: Indica-ting lamps are provided at the terminal stations and also at repeater stations remote from the terminal stations for indicating the direction of transmission for which the system has been conditioned under control of the direct current control signal. A switch associated with the rotatable picture scanning and picture reproducing cylinders at each station is provided for automatically stopping the rotation of the picture cylinders and simultaneously removing the direct current control from the system.

The transmission network which is used for picture transmission between stations is also utilized for transmission by telephone of necessary instructions in connection with the operation of the picture transmitting and receiving equipment, thus eliminating the expense of a separate communication channel for this purpose. The direct current control circuits are composited on the same wires that are used for picture and telephone transmission. In certain respects the transmission requirements are more severe for picture transmission than for telephone transmission. For example, relatively small abrupt changes in attenuation or transmission level of the transmission system which would have no noticeable effect on speech transmission, would be so noticeable in a picture reproduction as to render it unsatisfactory. In the present system, therefore, the direct current controi is utilized to prevent the operation of automatic gain control apparatus while a picture is being transmitted. vPoor quality of a picture reproduction is also caused by echo eiects on a line due, for example, to a slight unbalancing of a two-wire line at the two-way repeaters. For this reason the direct current control is also employed for controlling the repeater to prevent transmission through it in the direction opposite to the direction in which the picture is being transmitted. At bridging points where a plurality of transmission lines may be connected through a bridging network, short circuits are applied by means of the direct current control to all input circuits to the bridge except on the line transmitting the picture current into the bridge for the purpose of reducing the noise currents applied to the circuits and to increase the loss in the cross-talk paths. When a four-Wire circuit is connected to a twowire circuit, the connecting terminating equipment includes a lter for preventing singing when the circuit is used for two-way telephone transmission. This filter introduces sufficient delay distortion as to seriously impair the quality oi a picture reproduction. Rather than employing an expensive delay equalizer for correcting for this delay distortion, this lter is out out of the circuit under control of the direct control current when the circuit is used for picture transmission.

A picture broadcasting system embodying the invention will now be described in detail, reference being made to the accompanying drawings in which:

Fig. l shows the method of arranging the succeeding gures of the drawings; and

Figs. 2 to '7, inclusive, when arranged as shown in Fig. l, illustrate diagrammatically a complete picture broadcasting system.

Each of the terminal stations is provided with picture transmitting apparatus for producing an alternating current modulated in accordance with the tone values of successively scanned elemental areas of a picture, and picture receiving apparatus for utilizing the picture currents received from a distant station to control the exposure of the elemental areas in succession of a light sensitive picture reproducing surface in synchonism with the scanning at the transmitting point. Any number oi terminal stations may be provided and a picture may be transmitted from any station to all or any desired number of other stations, In order to avoid unnecessary repetition in the drawings, only three terminal stations are shown and the transmitting equipment is shown in detail only at station A of Fig. 2 and the receiving equipment is shown in detail only at station K of Fig. 7.

At the station A a picture I0 to be transmitted is mounted on the rotatable picture cylinder II. Light from source I2, after being interrupted by a light valve i3, energized by current from the alternating current source I4 of 2400 cycles, for example, is directed upon a small spot on the picture I0 and the light reected from this illuminated spot is received by the photoelectric cell i5. The scanning apparatus including the light source I2 and the photoelectric cell I5 is moved in the direction of the axis of the picture cylinder il as the cylinder rotates so that the elemental areas of the picture lying along a helical path are scanned in succession. The current set up in the circuit of the photoelectric cell is amplified in the amplier I6 transmitted through the bandpass lter I1 and equalizer I8 and further amplified by the amplifier I 9. This portion of the apparatus is disclosed in greater detail in U. S. Patent No. 2,041,822, granted to A. D. Dowd, May 26, 1936. The picture cylinder and scanning apparatus may be connected under control of an operator to a driving motor 20 by means of an electromagnetically operated clutch 2|. This clutch mechanism is described in detail in U. S. Patent No. 2,105,879, granted to C. C. Towne, Jan. .1.8, 1928. The motor 20, when started, operates continuously at a speed which is maintained accurately at a constant value under control of current from the source I4 of constant frequency alternating current and the speed control apparatus 22. This speed control apparatus is fully described in U. S. Patent No. 2,050,624, granted to E. R. Morton, Aug. 11, 1936. The apparatus at station A for operating the clutch magnet to start the picture cylinder II and the scanning apparatus, and for simultaneously sending out a signal for controlling the starting mechanism at the distant station is similar to that described in U. S. Patent No. 2,059,564, granted to A. D. Dowd, Nov. 3, 1936.

In order to transmit a picture from station A, the operator at this station closes the non-locking line-up key 23. This operation momentarily closes a circuit from ground through the adjustable stop switch 24, auxiliary stop key 25, through line-up key 23 through the Winding of relay 25 to grounded battery 21, thus causing the operation oi the relay. The relay locks up through its contact 28. The operation of this relay opens at its contact 2S the short circuit across the output of the picture terminal amplifier I9, thus permitting the picture carrier to be transmitted over the transmitting loop cf Which connects the local station with a central office B. The operation of the relay opens at contact 3D the energizing circuit for a receiving control relay 3i, thus preventing the energization of the receiving lamp 32, and closes at contact 33 a circuit from ground at 34 to the line h, for the purpose of sending out a direct control current from the central ofce to control apparatus along the transmission path to the distant stations and at the distant stations, thereby conditioning the system for picture transmission from station A only to the distant stations. The operation of relay 26 also completes a circuit at contact 35 for energizing a sending lamp 36 by current from battery 81, thereby indicating to the operator at station A that the system has been conditioned for picture transmission from station A. The operation of relay 23 also places a short circuit across the line-up switch 23 so that the transmission of a picture may be started When the non-locking start key 31 is operated. The operation of key 31 completes a circuit from grounded battery 38 through the Winding of clutch magnet 39 through contact 28 of relay 26 through auxiliary stop key 25 and the adjustable stop switch 24 to ground, thus operating the clutch magnet to start the movement of the picture cylinder II and its associated scanning apparatus. The magnet 39 locks up through its contact 40. When the start key 31 is operated and the clutch magnet 3S energized, the circuit which supplies current from the alternating current source I 4 to the light interrupting valve I3 is short-circuited through contact 4I of key 31 and contact 42 of clutch magnet 39, thus interrupting the transmission of carrier current over the line ef. This interruption in the transmission of carrier current exists only for a brief period While the key 31 is closed since the short circuit is removed due to opening of contact 4I when the key 31 is released. This brief interruption of the carrier current causes the starting of the picture receiving apparatus at the distant station and the picture which is scanned at station A is thus reproduced at the distant station. The auxiliary stop key 25 is provided to permit the operator to stop the picture transmitting machine and to remove the direct current control from the system at any time. When the picture I0 has been transmitted, the switch 24 mounted on the base of the picture transmitting machine is automatically opened thus stopping the machine by opening the energizing circuit for clutch magnet 39 and removing the direct current control from the system by opening the energizing circuit for relay 26.

When it is desired to reproduce a picture locally at the terminal station A the connector 43 terminated in plugs 44 and 45 is used to connect the local picture transmitting apparatus with the local picture receiving apparatus 46, this apparatus being terminated for this purpose in the jacks 41 and 48 respectively. The insertion of the plugs 44 and 45 in the jacks 41 and 48 disconnects the picture transmitting and receiving apparatus from the lines ef and cd, respectively, to the central oflice and also opens the circuit to ground34 so that ground will not be con.- nected to line h When the relay 26 operates. For transmitting a picture locally, it is necessary to operate rst the line-up key 23 so that the short circuit at the output of amplier IS will be opened at contact 29 and subsequently the start key 31 for starting the picture cylinder and scanning apparatus and interrupting the carrier current for starting the picture cylinder and scanning apparatus oi the picture receiving equipment.

Each terminal station is also provided with telephone transmitting apparatus 49 and telephone receiving apparatus 50. The keys 5I and 52 may be operated to connect the telephone transmitter and receiver to the lines ef and cd respectively and to disconnect the picture transmitting and receiving apparatus from the line. The telephone receiver may be of the loud-speaking type which is connected to the line by the operator as soon as a picture has been transmitted so that each station may be called in by an operator at any other station. The operator may then operate key 5I to connect in his telephone transmitter so as to carry on two-Way telephone communication With any other station.

At the central oice B the transmitting loop ef and the receiving loop cd terminate in the repeater equipment comprising ampliers 55 and 75 56,- hybrid coilA 51 andi balancing-'- network 58;l The repeater equipment-is connectedl-to acornposite set 54comprising repeating coi-159,- conu densers Sli-and 5| and inductance coils 52 and 63. The line ab'connects the composite set at central oiiice B with the-bridging repeater station C. When the operator at station Av operates-the line-up key 23 to -connect ground lto the line h the sending relay 64'at the central ofiice is en ergized by current from grounded battery 65 through a circuitincluding lcontact 66 of receiving relay 61. The operation ofrelay 64"closes a circuit at contact 68 to connect grounded bat- .tery 65 to line yb; If the line-up key 23 at station A has not been operated and the system has been conditioned at some distantA stationfor transmission from that station to other stations, including station A, a direct current transmitted over line a energizes'the receiving relay 61 to "open contact 66; thus disconnecting line hfrom the sending relay 64 to prevent the transmission of a control current from station A, and to conneet ground to the line h, thus causing the enrergization of relay 3| by current from grounded "5 battery BS at the central station. The operation of relay 3| closes a circuit to cause the lamp 32 to be energized by current from battery.

Station C of Fig. 3 is a bridging or switching station equipped with apparatus to permit an '39' operator to connect together any number of twowire lines terminating at this station. There is also associated 'with station C a terminal station D equipped like station A for transmitting and receiving pictures and for transmitting and receiv- CFI ing speech. The line ab from central oice B is connected to a composite set |00 vlike the set 54 at central oice B. The composite set is connected to a repeater comprising hybrid coil ii, ybalancing network |52, potentiometer- H33 and empliiiers E04 and |65. When the locking key |66 is operated, a circuit is completed or'energizing relay ifi? by current from grounded batteryV 552,019,603, granted to C. W. Green, Nov. 5, 1935.

A terminal station D similar to terminal station A comprising picture transmitter i0, picture receiver telephone transmitter H2, and telephone receiver i3 is also connected to the bridg- 1"ing network through the one-way ampliers H4 and H5. When the relay H6 is-energized by current from battery l1 due to the operation of locking key 24 the-two-wire line ik is connected to the bridging network |39 through the com- F' posite set |9, and a two-way repeater comprising the hybrid coil |20, balancing network |2| and ampliers |22 and |23. When key H8 yis-operated to cause the energization of relay |25, twowire line lm is similarly connected to the bridging circuit E09 through composite set |26 "and a two-way repeater comprising hybrid coil |27, balancing network |28 and amplifiers |29 and |36.

Assuming for the present that keys |636, H8

and |24 are operated to connect lines ab, :ik and ing'ifof the "line-up key '23 at station A will cause thes'endingrelay 64 at central stationB tooperate; thus connecting battery E5 to line b, Current from source 'Bi'i'will thus operate sending relay-|3|`-at station C to open the venergizing circuit-for receiving relay |32 at contact |33 and to connect grounded battery |34 to the winding of relay 135i causing it to operate. With relay |35 operated,l ground is connectedthrough switch |24fwhe'n operated, to the Winding of sending relay'fl3'l', thus causingit to be energizedby current from grounded battery |38. The operation of trelay |37 completes an energizing circuit for sending'lamp |39 and connects grounded battery|38"to line'y'. The operation of relay I3?l also applies a short lcircuit to the input of ampliiier"|2`3. Similarly, due to the operation of relay ground' is connected through switch ||8;"when operated, to the winding of sending relayl thus causing it'to be energized by cur- Zm alltothe bridging network |09,fthen the closrent from grounded battery it. The operation of relay y|36 completes an energizing circuit for sending lamp |4| and connects grounded battery |40to line'l. The operation of relay |35 also applies a short circuit to the'input circuit' of amplifier |3. Thus the operator at station 'A may condition the system for transmitting pictures from station A to station D and to the stations connected to bridging station C by lines ik and Im. If the switch I8 at bridging station C is not' operated there will be no transmission to the station connected to line lm and if the'switch |24 is not operated there will be no transmission to the station connected to line ik. By opening switch lil and closing switches IIB and |24 station A will be disconnected from the system and the stations associated with line jk will"be"connected with the station associated with line lm and also with station D. Of course, a larger number of lines, such as ab, ik and lm maybe connected to the bridging network it if desired'and an operator at station C may connect anydesired combination of lines into the system."

If an operator at some distant station connected Y tol line jk Wishes to transmit a picture, grounded battery is applied to line lc to cause the operation of relayVY |42. The operation of relay |42 applies grounded b-attery'iS to relay |35 to cause it to operate, switch |24 being closed, The operation of relay |42 opensl the energizingcircuit for relay |31 so that battery cannot be applied to line j. If switch H8 is closed ground is applied to the winding of Yrelay ISS to cause its energization by grounded battery i4@ and the operation of relay 36 causes theV lamp |45 to be energized and grounded battery Ha to be applied to line l. If switch it is closed, the operation of relay |35 will also cause ground to be applied to the winding of relay H|32 to cause' it to operate, thus energizing lamp"|4'4` and applying grounded battery |45 to line e. Grounded battery applied to line a will operate relay 61 to apply ground to relay 3| to cause it to operate to energize receiving lamp 32 at station A. In the same way a station connected to' line lm may control other stations in the system by causing the energization of relay |46 by grounded battery applied to line m.

The apparatus connected to liney lm is not shown, but may be similar to that connected to line 77C which will now be described. The system may employ both two-conductor, open-wire transmission lines such as ab, ik, and lm and also fourwi're cable circuits such as nopq. Fig. 4 shows a ltO repeater station E equipped with apparatus for connecting two-wire line :ik to four-wire cable circuits nopq. Line ik is connected to the composite set 200 like the composite set 54. The composite set 200 is connected to atwo-Way repeater comprising hybrid coil 20|, balancing network 202, attenuation network 203, lter 204 and amplifiers 205 and 206. Amplifier 205 is connected through composite set 201 to the outgoing conductor no and amplifier 206 is connected through composite set 208 to the incoming conductor pq. If the operator at station A, for example, operates the line-up key 23, grounded battery is supplied to line i, as previously described, and relay 200 is operated. The operation of relay 209 supplies ground to relay 2|0 to cause it to be energized by current from grounded battery 2| I. energization of sending lamp 2 I2, causes the input of amplifier 206 to be short-circuited and connects positive battery to line q and ground to line p. When positive battery is connected to line n and ground to line o by means of a relay similar to relay 2 I 0 at the distant end of line nopq, relay 2 I 3 operates to open the energizing circuit of relay 2 I 0 and to connect ground to relay 2| 4, causing its operation by current from battery 2|5. Battery 215 is thus supplied to line k to control apparatus at bridging station C as previously described. The operation of relay 2 I4 also causes the energization of lamp 2|6 and causes ground to be applied to relays 2I1, 2I8 and 2|9 which are thus operated by curent from battery 220. The operation of relays 2|`| and 2|8 connect amplier 206 directly with the hybrid coil 20|, disconnecting filter 204 from the circuit. The operation of relay 2|9 places a short circuit on the input of amplifier 205. Fig. shows a repeater station F on the cable circuit npq equipped with automatic gain control apparatus or pilot wire regulator 300. A simple type of pilot wire regulator is shown for illustration, but other types of pilot wire regulators may obviously be employed. For example, a regulator of the type shown in U. S. Patent No. 2,017,654, granted to J. A. Coy and H. I. Romnes, Oct. 15, 1935, may be used. For convenience in describing the circuit, the four-Wire cable is labeled nopq where it enters the repeater station and rstu where it leaves the repeater station. The pilot wire z consists of two conductors parallelling the four-wire cable and short-circuited at its ends. In practice a plurality of repeater stations employing pilot wire regulators are used on a long cable. The cable conductors no are connected through composite set 30|, variable attenuating network 304 of the pilot wire regulator 300, ampliner 302, and composite set 303 to the conductors rs of the cable. Similarly, the cable conductors pq are connected through composite set 305, the variable attenuating network 308`of the pilot wire regulator 300, one-Way amplifier 306, and composite set 30'! to the conductors tu of the cable.

The pilot wire z which may extend from station E to the repeater station G of Fig. 6, for example, forms a loop which is connected into one arm of the Wheatstone bridge 3|0. AThe opposite arm of the bridge consists of a variable resistor 3| I. Battery 3|2 is connected across two opposite vertices of the bridge and a polarized relay @i3 is connected across the other vertices of the bridge. A motor 3M which drives the arm of the variable resistor 3|| and the arms of variable attenuators 308 and 304 is energized in one direction or the other by current from source 3|5 depending on the direction of the cur- The operation of relay 2|0 causes thel rent in the bridge circuit through the winding of polar relay 3| 3. When there is a change in attenuation of the pairs of the cable no and pq, due to temperature changes, for example, there is a corresponding change in resistance of the pilot wire z of the cable. As a result the bridge 310 will be unbalanced to cause the operation of relay -3l3 and motor 3M in one direction or the other depending upon whether the resistance of the pilot wire has increased or decreased. The motor will operate to change the setting of variable resistor 3II until the bridge balance is restored and the settings of variable attenuators 308 and 304 will be changed to add or take out attenuation to restore the overall attenuation of the cable circuit to the normal value. However, a sudden change in the attenuation such as is produced by changing the setting of variable attenuators 303 and 304 is not desired when a picture is being transmitted since such a change in attenuation would result in one part of the picture reproduction being noticeably of darker tone value than another portion although no such change in tone value is present in the original picture. For this reason the energizing circuit for motor 3M is opened under control or the direct control current when a picture is about to be transmitted. When relay 2I0 at station E operates to connect positive battery to line q and ground to line p, polar relay 3I5 is operated to apply ground to one terminal of a winding of polar relay 3|? and the relay 3|I will operate to close contact 3|8 which completes the energizing circuit for relay 3|9 and thus causes the relay 3|9 to operate to open the energizing circuit for motor 3HE. If relay 3|8 should be accidentally released for a period less than two seconds, as would occur, for example, due to the grounding of line y connecting station A with central office B for a short period, the condenser 20 would merely partly charge during this interval and the relay 3I'l would not release. In the same way when positive battery is applied to conductor 'r and ground to conductor s, as would be the case when a picture is being transmitted in the opposite direction from that assumed above, relay 32| Will operate to connect ground to a terminal of winding of relay 3|? to operate it and thus cause the operation of relay 3|8 which opens the energizing circuit for motor 3M.

Fig. 6 shows a repeater station G like the repeater station E of Fig. 4 for connecting the four-wire cable rstuv to the two-conductor openwire line vw. The apparatus at station G has been numbered to correspond with the numbering of the corresponding parts at station E with the exception of the rst digit. At station G the numerals applied to the apparatus extend from 500 to d20 while at station E the corresponding apparatus is numbered from 200 to This apparatus requires no further detailed description.

There is also shown in Fig. 6 a bridging station H like the bridging station C of Fig. 3. The two-wire line 'uw going to station G, my going to central office J of Fig. l and lines 450 and 450, which go to other stations notshown, are connected into the bridging station H.

The central oilce J of Fig. '7, like central oillce B of Fig. 2, is connected to the two-wire line my. Line xy is connected through the composite set 554, like composite set 54 at station A, and a two-way repeater comprising hybrid coil 55T, balancing network 553 and one-way amplifiers 555 and 556.

The picture sending apparatus 510 at the terminal station K is connected through jack 55| and key 541 to the loop ef which is connected to the amplifier 555 at the central ollce J. The loop cd which connects the amplifier 556 With the local station K is connected through key 548 and jack 552 to amplier 51|, band-pass filter 512, amplier-recvalues of elemental areas of the picture are re- 1 produced in succession along a helical path in synchronisrn with the scanning of the elemental areas of a picture at a transmitting point, station A for example. This portion of the picture reproducing apparatus is disclosed in greater detail in Patent No. 2,041,822 supra. The

clutch mechanism is described in detail in Pat- The motor, 580, when ent No. 2,105,897 supra.V started, operates continuously at a speed which is maintained accurately at a constant value under control of current from source 5|4 of constant frequency alternating current, having the same frequencies as the source I4 at station A, and the speed control apparatus 522. This speed control apparatus is fully described in the patent of E. R. Morton, supra.

The arrangement for operating the clutch 58| so as to start the picture receiving apparatus substantially simultaneously with the picture transmitting apparatus under control of a transmitting operator at station A, for example, is described in detail in Patent No. 2,059,564, re-

ferred to above.. When the non-locking start key 582 is momentarily operated by the attendant.

at station K, the Winding of relay 583 is energized by current from grounded battery 584. l. The operation of relay 583, which locks: up

through contact 585, removes a short circuit across the lower Winding of polarized relay 585 Relay v causing it to operate to close contact 581. 588 is thus operated by current from battery 589 and this relay is locked up by current from battery 554. The operation of relay 563 comp-letes the circuit from. ground through adjustable stop tion A, for example, the carrier current supplied to the loWer Winding of relay 585 is momentarily l interrupted. This causes the relay 585 to operate to close contact 592 thus completing the circuit to grounded battery 589 and energizing the clutch magnet 59| to start the receiving machine;

When the operator at station A, for example,

operates the line-up key 23 battery is connected to line .r to cause the operation of relay 561 at the central oiiice J.

563. gized by current from battery. causing the energization of lamp 532, the relay The lamp 532 is thus caused to be ener- 53| may obviously perform some other function" which may be desired to condition the receiving 'ceiving apparatus to the central stations. 'ator K 'will adjust the adjustable stop contact Ground is thus connectedto one terminal of the Winding of relay 53| to` cause it to be energized by current from battery r In addition to station for receiving a picture. 'Ihe connector 543 may be used to connect the picture transmitting and receiving apparatus at station K for reproducing a picture locally, as at station A. Station K, like station A, is also provided with Atelephone transmitting apparatus 549 and telephone vreceiving apparatus 550. tier 513, low-pass filter 514 and light valve WTO review the operation of the complete sys-- tem, assume-now that the operator at station A t wishes to transmit a picture to a number of other `stationsincluding station K. He will rst oper- Aate switches'5l and 52 and announce into the telephone transmitter 49 that the operators. at

the other station should p-repare the apparatus at their station to receive a picture. If desired the operator' at station A may also operate the line-upkey 23 at this time so that a visible signal Ais produced at the station K for calling the operator. In this case the auxiliary stop key 25 must 'be subsequently operated if it is desired to restore the'system for two-Way telephone communication. vIf the operator at station K is not ready to receive a picture, or if, for any other reason, he lWishes to communicate with station A, he Will operate his talking key 541 so that he may carry on two-Way telephone communication withthe operator at station A. When operator A has given vthe necessary instructions as to the size of the picture to be transmitted, for example, the operators Will restore keys 5|, 52, 541 and 548'to connect the picture transmitting and re- Oper- 589 onthe base of the receiving machine, operator A having previously set the adjustable stop "con'ta'ct24:Y close the line-up key 23.

Operator A Will now momentarily Sending relay 26 Will thus be locked up toremove the short circuit from the lOutput of picture terminal amplifier i9, to energize sending lamp 36, to open the energizing circuit-'to receiving relay 3| and to compl-ete the energizing circuit vfor sending relay 64 at the central ofiice B.v The operation of relay 54 will connect grounded battery to line b going to the bridging repeater station C Where the direct currenttransmitted over line b Will operate sending relay |3|'." The switches |05 and |24 at station C having been' operated, the operation of relay |3| Will lcause the energization of relay |35 to place ground on one terminal of Winding of relay |3'E, causing it to operate. The operation of relay |31 will cause the lamp |39 to be energized to indilto increase'the loss of the cross-talk paths. The

operation Yof relay `|3V1Will also cause battery to be applied to line y'. f

At-repeater'station E the direct current transmitted'over llin'en` will operate receiving relay 259l to open the energizing circuit of sending relay 2l'4 and to apply ground to Winding of relay 2i0`causing it to be energized. The operation of relay-2m will cause the lamp 2|? to be energized to indicate that the circuit is conditioned "fofr `transmitting from line ik to four-Wire cable circuit nopq.- Relay 2| when operated will also place a"short circuit on the rinput of amplier '206 to`A prevent echo elcta The operation of ill relay 2 I 0 will also place positive battery on line q and ground on line p to cause the operation of relay 3|6 at repeater station F.

The operation of relay 3|6 will cause the energizing circuit for motor 3|4 to be opened by contact of relay 3|9 to prevent the operation of the automatic gain control apparatus including Variable attenuators 308 and 304. The current which operates relay SI5 flows through lines t and u to cause the operation of relay 4|3 at repeater station G. The operation of relay 4|3 will open the energizing circuit for relay 4|!! and connect ,ground to winding of relay 4 |4 to cause its operation. The lamp 4|6 is thus energized to indicate that transmission is from the four-wire cable circuit rstu to two-wire line vw. The operation of relay 4|4 will also cause ground to be connected to the circuit including relays 4|'|, 4|8 and 4|9 causing these relays to be energized. The relay 4| 9 when operated short-circuits the input to amplifier 405 to reduce noise currents on the line and to prevent singing and the operation of relays 4|? and 4|8 will disconnect filter 404 from the transmission path. This lter is required in the circuit for two-way speech transmission to prevent singing but is not required when a picture is being transmitted in one direction on the circuit. The ilters if allowed to remain in circuit when pictures are being transmitted would introduce sufcient delay distortion to lower the quality of a picture reproduction considerably. The operation of relay 4|4 will also connect grounded battery 4|5 to line o. At bridging station H, relays corresponding to relays |3|, |35 and |31 of bridging station D will operate and grounded battery will be connected to outgoing line :z: thus causing the operation of relay 56T at central o'ice J. The operation of relay 561 connects ground to the winding of relay 53| at terminal station K to cause lamp 532 to be energized, thus indicating to the operator at station K that the system has been conditioned for picture transmission to his station.

The operator at station K then operates the non-locking start key 582 to condition the starting circuit as previously described. TheV operator at station A then operates the start key 31. This causes the energization of clutch magnet 39 at station A to start the operation of the picture transmitting machine and momentarily interrupts the carrier current transmitted to station K. At station K the interruption of the received carrier` current causes the operation of clutch magnet 59| to start the picture receiving machine. When the operator at station A releases the non-locking start key 31, the carrier current is again transmitted and, due to the operation of the picture transmitting machine, this carrier current is modulated in accordance with the tone values of successively scanned elemental areas of the picture. At station K the received picture current, after being ampliiied and rectiiied, actuates the light valve 516 to control, in succession, the exposure of the elemental areas of the light sensitive surface 578 to reproduce the picture thereon.

When the picture has been transmitted the automatic stop 24 mounted on the base of the picture sending machine at station A automatically opens the energizing circuit for the clutch magnet 39 to stop the picture sending machine and opens the energizing circuit for relay 26 to remove the direct current control from the system, thus restoring the system for two-way telephone communication. The automatic stop 524 at station K will also operate to stop the picture receiving machine. An operator at any other station may now condition the system for broadcasting pictures from that station.

In the picture broadcasting system as :described, the direct control current performs ce1'- tain specic operations for conditioning the system for one-way picture broadcasting. Obviously, however, the direct control current may be utilized to perform functions, other than those specically described, which may be found necessary in any system which may be set up.

What is claimed is:

1. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive current from any of said lines and distribute it simultaneously to the others of said lines, means at each of said stations for controlling the transmission of control impulses other than the signaling impulses simultaneously to each of the other stations, and means at each of said stations to condition apparatus thereat under control of said impulses transmitted under control of any other of said stations.

2. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive current from any of said lines and distribute it simultaneously to the others of said lines, circuit control means at each of said stations in addition to said signal transmitting and receiving apparatus for controlling the transmission of control impulses simultaneously to each of the other stations, and means at each of said stations to condition apparatus thereat under control of said impulses transmitted under control of another of said stations.

3. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive signaling current from any of said lines and simultaneously distribute it to the others of said lines, two-way repeaters in said lines respectively, and means at each of said stations for controlling the transmission of control impulses other than the signaling current to simultaneously condition all of Said two-way repeaters.

4. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive current from any of said lines and simultaneously distribute it to the others of said lines, a two-way repeater in at least one of said lines, circuit control means at each of said terminal stations for controlling the transmission of direct current impulses simultaneously to each of the other stations, and means at each of said stations to condition apparatus thereat under control of said direct current impulses transmitted under control of another of said stations.

Y 5. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive current from any of said lines and simultaneously distribute it to the others of said lines, a two-way repeater in at least one of said lines, means at each of said stations in addition to said signal transmitting and receiving apparatus for controlling the transmission of direct current control impulses simultaneously to each of the other stations, direct current repeating apparatus associated with each of said two-way repeaters for repeating said direct current impulses, and means at each of said stations to condition apparatus thereat under the control of said direct current impulses transmitted under control of another of said stations.

6. A signaling system comprising three or more stations, signal transmitting and receiving apparatus at each of said stations, an impedance network, connecting lines associating said impedance network with said stations respectively, said network being adapted to receive current from any of said lines and simultaneously distribute it to the others of said lines, two-way repeaters in each of said lines adjacent said network, circuit control means at each of said stations for controlling the transmission of control impulses other than the signaling current simultaneously to each of the other stations, means at each of said two-Way repeaters under control of said control impulses for conditioning said repeaters for one-way operation, and means at each of said stations for conditioning apparatus thereat under control of said impulses transmitted under control `of another of said stations.

7. An image broadcasting system comprising three or more stations, signaling means at each of said stations for transmitting image current to each of the others of said stations simultaneously, image receiving means at each of said stations, means at each of said stations for controlling the transmission of control impulses other than the signaling current to each of the other stations simultaneously, and means at each of said stations for conditioning the apparatus thereat under control of said impulses transmitted under control of another of said stations.

ALLAN WEAVER. 

